Olefin pyrolysis process promoted with mixtures of bromine and aromatic hydrocarbons



United States Patent 3,388,183 OLEFIN PYROLYSIS PRGCESS PROMOTED WllTll-I MIXTURES OF BROMINE AND ARO- MATIC HYDROCARBONS Kenneth J. Frech, Tallmadge, Ghio, assignor to The Goodyear Tire & Rubber Company, Akron, ()hio, a corporation of Ohio N0 Drawing. Continuation-impart of application Ser. No. 399,068, Sept. 24, 1964. This application Aug. 17, 1966, Ser. No. 572,905

Claims. (Cl. 260-680) ABSTRACT OF THE DISCLOSURE Olefins are cracked using as the cracking promotor a mixture of a bromine containing compound and benzene, toluene or xylene. Increased yields and efficiencies are shown for the preparation of isoprene from 3-methyl-2- pentene by the use of hydrogen bromide with benzene and toluene as the cracking promotor.

This application is a continuation-in-part of Ser. No. 399,068, filed Sept. 24, 1964 which was, in turn a continuation of Ser. No. 218,169, filed Aug. 20, 1962, all of which are now abandoned.

This invention relates to an improved process of olefin pyrolysis employing certain materials as pyrolysis promotors.

It is known that certain olefins may be thermally decomposed or cracked by subjecting them to elevated temperatures, for instance olefins which have in their molecular make-up a carbon-carbon bond which is in a position beta to the double bond will, under proper conditions of heat, time and pressure, undergo a scission of the carbon-carbon bond in the position beta to the double bond. By the terms cracking, decomposing, cracked, or decomposed as employed throughout this specification and claims is meant that the olefin molecule splits into two or more fragments at the carbon-carbon bond which is in a position beta to the double bond. This will be explained in more detail later.

The thermal decomposition or cracking of olefins is usually conducted in a closed zone or reactor and is usually conducted in the absence of oxygen. The temperatures employed usually vary from about 300 to about 1,000 C. Usually this thermal cracking process is conducted while the olefins are in a gaseous state. The olefins may be cracked in relatively pure form or a diluent may be employed.

Employing the most favorable conditions conducive to the cracking of olefins, these conditions being temperature, residence time in the cracking zone, the ratio of the olefin to the diluent if any be employed, it has been found that olefins decompose in fairly low yields and at fairly low efficiency. As employed in this application the term yiel is meant to connote the decomposition of the olefin feed stock per pass through the cracking zone and the term efficiency is meant to connote the total decomposition to the desired end product when employing conventional recycle techniques.

It is therefore the object of this invention to provide a method whereby the per pass yield of the desired products produced by cracking these olefins is increased. Another object is to increase the ultimate yield or efiiciency of the desired product. Another object is to provide a .method whereby the residence time in the heating zone and the temperature of the heating zone may be decreased to prevent undesirable side reactions from taking place. Still other objects are to provide cracking promotors which 3,338,183 Patented June 11, 1958 will allow greater yields and greater efiiciencies to be obtained in the cracking of these olefins. Still other objects will be apparent as the description proceeds.

To further explain what is meant by a carbon-to-carbon bond in a position beta to double bond, the following discussion is intended to be illustrative and not restrictive of the scope of this invention. The particular materials which predominate when olefins are cracked depend largely upon the configuration of the particular olefin. By configuration is meant the location of the double bond and the location of the side group in chain, if any. It is believed that this best can be illustrated by the following discussion. When an olefin containing 6 carbon atoms with a side group, i.e. a methyl group, attached to the second carbon atom of the main or straight portion of the chain, and the double bond in the 2 position, such an olefin being 2- methyl pentene-Z, is subjected to cracking conditions, the predominant products obtained ar Z-methyl butadiene-1,3 (isoprene) which is a diolefin, and methane, a paraffin. On the other hand if a 6 carbon olefin such as 2-methyl pentene-l, which has the double bond in the 1 position and the methyl group in the 2 position, is cracked, it will yield as predominant products two other olefins, isobutylene and ethylene. When still another isomeric hexene such as 4 methyl pentene-l is cracked, two moles of propylene are formed. These differences in products obtained, when different isomeric forms of olefins containing the same number of carbon atoms are cracked, ar due to the fact that olefins crack at the position beta to the double bond. That is to say, the carbon-carbon bond which is two carbon atoms removed from the double bond, is the carbon-tocarbon bond at which the scission occurs. There are certain olefins which do not contain in their molecular makeup a carbon-carbon bond in the position beta to the double bond and, therefore, do not undergo the same reactions when subjected to thermal decomposition conditions. These olefins are ethylene, propylene, butene-Z, isobutene, 2- methyl butene-Z, and 2,3-dimethy-l butene-2, and are usually referred to as refractory olefins. Since these olefins do not undergo similar chain scission as do olefins which contain in their molecule a carbon-to-carbon bond in the betaposition to the double bond, these refractory olefins are not considered to be within the scope of the olefins which are to be cracked in accordance with this invention.

It has been found that the objects of this invention are accomplished by subjecting olefins which have in their molecules a carbon-carbon bond which is in a position beta to the double bond to conditions of temperature and suitable or suflicient to cleave the carbon-to-carbon bond in the position beta to the double bond while in the presence of a promotor which comprises a mixture 'of bromine and at least one aromatic hydrocarbon selected from the group consisting of benzene, toluene and Xylene.

The practice of this invention may be carried out in any conventional manner which is usually employed in the thermal cracking of olefins.

Generally, the conditions which may be employed in the practice of this invention may vary widely, for instance the cracking temperature may vary broadly from about 400 C. to about 900 C. However, more preferred cracking temperatures are from about 600 C. to about 750 C. The time in which the olefins are in the cracking zone may range broadly from about 0.001 to about 3.0 seconds. However, it is more preferable to employ times varying from about 0.05 to about 0.5 second. These times which are referred to are usually called residence times and are defined as the time required for one molecule of gas whether it be pure olefin or in mixture with the diluents to pass through the cracking zone.

As was stated above, generally olefins are cracked either as pure hydrocarbons or as mixtures with other diluent gases. These diluent gases may be such materials as steam, carbon dioxide, hydrogen, parafiins, the refractory olefins, or any other inert gaseous substance which powder which was microspheroidal silica-alumina cracking catalyst. The heat transfer powder was heated both by electrical resistance heaters and by combusting a natural gas flame in the fluidized powder bed. The temdoes not materially affect the cracking process or react 5 perature gradient from top to bottom of the bed was with either the feed stock or products other than to act never more than 5 to 6 C. and the gradient from the generally as a diluent. The ratio of this diluent gas may fluidized bed to the tube walls was about 5-6 C. The be widely varied depending on conditions, but it is usually temperatures within the fluidized bed were measured by employed in mol ratios of from 0.5/1 mole of diluent conventional thermocouple techniques as were the temper mol of olefin to 15/1. If more than about 15/1 mol 10 peratures within the cracking zone. The procedure emratio is employed, the process tends to become uneconomployed was to bring the heat transfer powder up to about ical. Therefore, it is preferred to use a diluent to olefin 500 C. employing the electrical resistance heaters while mol ratio ranging from about 2/1 to about 4/1. fluidizing the heat transfer powder with air. Then the The pressure employed in the cracking zone may be natural gas burner was employed to bring the heat transvaried from a low of 10 milliliters of mercury to 500 fer powder up to the desired cracking or operating tempounds per square inch gauge or even higher. However, it perature. When toluene and benzene was used in these is usually preferred that the pressure range from about experiments, it was added to the olefin feed stream. The atmospheric to about 100 p.s.i. with about 1-2 atms. being bromine and/or hydrogen bromide were added separatepreferred. 1y to the cracking reactor. The water and the olefin feed As was stated before, the activator or promoter emstream were pumped at the proper rates necessary to ployed in this invention to promote the cracking of produce the H o/hydrocarbon ratio desired and to give olefins is a mixture of bromine and hydrocarbons sethe desired residence time Of the materials in the cracking lected from the group consisting of benzene, toluene and zone or cracking reactor. When all variables had been xylene and/or mixtures thereof. The bromine component adjusted to give the desired operating conditions the of this promoter may be supplied either in gasous form products resulting from the cracking operation were or as a liquid under pressure. In addition to bromine itcollected by means of cooled receivers, if liquid, and were self any organic or inorganic bromine containing commetered at atmospheric and room temperature condipound may be employed. Representative of such comtions, if gas. The products were analyzed for content and pounds are ammonium bromide and hydrogen bromide. yields by conventional analytical methods. Conventional The promoter may be added to the feed stock in various 3 recycle techniques were employed to obtain the ultimate ways, however, it is usually found convenient to dissolve yield. these materials in the ol fin to be cracked. Other methods The results of each of the experiments in the fol- Which may be employed are to feed the promoter mixture lowing examples as well as the operating conditions are or even the promoter components separately into the reported in tables below. Column 1 is the experiment cracking furnace along with the olefin and diluent, if any number; column 2 is the residence time in seconds; colare being used. umn 3 is the temperature employed in the cracking op The amount of promoter employed i th ti f eration in degrees Centigrade; column 4 is the material this invention has not been found to be too critical. p y as the Particular Cracking Promoter With the Of course, sufiicient promoter should be employed to amount p y in mol lfthlcent based on the Olefin t0 cause an effect and for the sake of economy no more be cracked (Where 110 Promoter Was p y this pr otershculd be employed than is necessary. Genumn lists none); column 5 is the mol percent yield of erally, it has been the practice to employ at least 2.0 mol isoprene per pass based on the 3-methyl pentene-Z percent of promoter calculated as the bromine component. Charged; Column 6 is reaction eihciehcl of ultimate Usually, at least 2.0 mol percent of the hydrocarbon comyield and is the amount of isoilrehe Obtained based 0h ponent of the promoter is used. The ratio of the hydrothe 3'methyl pehtenerz Charged using COhVehtiOhfil carbon component of the promoter to the bromine com- Cycle techniquesponent may vary widely and has not been found to be E AMPLE critical. A ratio of from about 1/1 to about 20/1 is In this example 3-methyl-2-pentene was the olefin emusually p y A150 it has been found thathtfle, if y, ployed. A diluent, steam, was employed at a mol ratio further improvement is obtained when more than mol 50 of approximately 3.2/1, steam to hydrocarbon. In these percent of the bromine component is employed. (All experiments No. 1 illustrates the effect of true thermo mol percentage calculations are based on the total mols cracking; 2, 3 and 4 illustrate the effect of toluene alone; Ofthe Olefin t0 be k 5 illustrates the use of hydrobromide alone; experiments The practice of this invention is illustrated by the 6-11 illustrate the practice of this invention and the imfOllOWiIlg experiments which are to be interpreted as provcment obtained thereby.

Time Temperature Promoters Yield Elliciency 15 575 17. s (an. 0 .15 575 17. 1 00. 5 15 675 15. 2 8n. 7 .15 675 12.2 55.0 10 077 40. 6 n3. 5 .14 575 38.4 73.4 15 676 38. 2 75. 0 15 075 40. 2 78. s .15 575 32.8 76.3 15 575 37. 1 73. 4 15 575 31). 1 70. 5 'Iol.=Toluene.

Ben.=l3cnzene. HBr=1-Iydrogen Bromide.

representative rather than restrictive of the scope of this invention. The results and conditions of the cracking experiments are reported in table form.

All of the cracking experiments were performed in a reactor assembly consisting of a hairpin coil prepared from A-inch OD. 316 stainless steel tubing. This coil reactor was immersed in a bed of fluidized heat transfer mm the above example it can be readily seen that the 0 catalyst of this invention as exemplified by Runs 5 through 11 show a distinct improvement over hydrogen bromide alone (Run 5) and toluene alone (Runs 2, 3 and 4), as well as true thermal cracking (Run 1). Other similar results may be obtained when the general techniques of these examples and the other specific conditions mentioned elsewhere in this application are applied to other olefins.

The list of olefins set forth below is representative of the olefins, the cracking of which may be enhanced by the promoter of this invention.

Representative among the olefins which will decompose to form predominantly butadiene-1,3 when cracked in accordance with the practice of this invention are pentene-Z; hexene 2; 3-methyl pentene-l; cyclohexene; 3- methyl butene-l; Z-heptene; S-methyl heXene-l; S-methyl hexene-2; 2-octene; 5-methyl heptene-2; 3,5-dimethyl heXene-l; 3,4,4-trimethy1 pentene-l; 6-methyl heptene-2; nonene-Z; and 3-methyl octene-l.

Representative among the olefins which will decompose to form predominantly Z-methyl butadiene-1,3 or isoprene when cracked in accordance with the practice of this invention are Z-methyl pentene-2; 3-methyl pentene- 2; 2-ethyl butene-l; 3,3-dimethyl butene-l; 2,3-dimethyl butene-l; 2-methyl hexene-2; 3-methyl hexene-2; 2-ethyl pentene-l; 2,3-dimethyl pentene-l; and 3,3-dimethyl pentene-l.

Representative among the olefins which will decompose to form predominantly 2-ethyl butadiene-1,3 when cracked in accordance with the practice of this invention are 3-ethyl pentene-2, 2-ethyl pentene-Z and S-ethyl heXene-Z.

Representative among the olefins which will decompose to form predominantly 2,3-dimethyl butadiene-1,3 when cracked in accordance with the practice of this invention are 2,3-dimethyl pentene-2; 3-methyl-2-ethyl butene-l; 2,3,3-trimethyl butene-l; 2-isopropyl pentene-l; 2,3,3-trimethyl pentene-l; and 2,3-dimethy1 heptene-2.

Representative among the olefins which will decompose to form predominantly 3-methyl pentadiene-1,3 when cracked in accordance with the practice of this invention are 3-methyl heptene-3; 3,4-dimethyl hexene-Z; and 3,6-dimethyl heptene-3.

Representative among the olefins which will decompose to form predominantly 2-methyl pentadiene-1,3 and 4- methyl pentadiene-1,3 when cracked according to the practice of this invention are 2,4-dimethyl pentene-Z; Z-methyl heptene-3; 4,4-dimethyl heXene-Z; 2-propyl pentene-2; 2- methyl-B-ethyl pentene-l; 2,6-dimethyl heptene-3 and 2- propyl hexene-l.

Representative among the olefins which will decompose to form predominantly piperylenes when cracked in accordance with the practice of this invention are heXene-3; 4-methyl pentene-Z; heptene-3; 4-methyl hexene-2; octene- 3; 4-methyl heptene-Z; 6-methyl heptene-3; 3-ethyl hexene-l', 4-methyl-3-ethyl pentene-Z; 4,5-dimethyl heptene- 2; and 4,5,5-trimethyl heXene-2.

While certain representative embodiments and details have been shown for the purpose of illustrating the invention, it will be apparent to those skilled in this art that various changes and modifications may be made therein without departing from the spirit or scope of the invention.

What is claimed is:

1. A promoted pyrolysis process which comprises providing a mixture of (1) at least one olefin selected from the group consisting of pentene-2, hexene-2, 3-ethyl pentene-2; 2-ethyl pentene-Z; 3-ethyl heXene-Z; heXene-3; 4-methyl pentene-2; heptene-3; 4-methyl hexene-Z; 2,3- dirnethyl pentene-2; 3-methyl-2-ethyl butene-l; 2,3-

dimethyl heptene-2; 3,4-dimethyl hexene-2; 3-methyl heptene-3; 2,4-dimethyl pentene-2; 2-methyl heptene-3; 2- propyl pentene-2; Z-methyl pentene-2; 3-methyl pentene-2; 2-ethyl butene-l; 2,3-dimethyl butene-l; Z-methyl hexene-Z and 3-methyl hexene-Z characterized in that they contain in their molecule a carbon to carbon single bond in a position beta to the double bond and (2) a cracking promoter consisting essentially of a mixture of (a) at least 2 and not more than mole percent of a bromine containing compound selected from the group consisting of hydrogen bromide and ammonium bromide based on the olefin and (b) at least 2 mole percent of at least one hydrocarbon selected from the group consisting of henzene, toluene and Xylene based on the olefin, the mole ratio of (b) to (a) ranging from 1 to 1 to about 20 to 1, and cleaving these carbon-to-carbon single bonds, which are in a position beta to the double bond of said olefins, by subjecting said mixture to temperatures ranging from about 600 C. to about 750 C. for periods of time ranging from about 0.05 to about 0.5 second.

2. A process according to claim 1 in which the bromine containing compound is hydrogen bromide.

3. A process according to claim 1 in which the olefin is at least one selected from the group of pentene-Z and hexene-Z, thereby producing a predominance of butadiene- 1,3.

4. A process according to claim 1 in which the olefin is at least one selected from the group of 3-ethyl pentene- 2; 2-ethyl pentene-Z and 3-ethyl hexene-Z, thereby producing a predominance of 2-ethyl butadiene-1,3.

5. A process according to claim 1 in which the olefin is at least one selected from the group of heXene-3; 4- methyl pentene-2; heptene-3 and 4-methyl hexene-2, thereby producing a predominance of piperylene.

6. A process according to claim 1 in which the olefin is at least one selected from the group of 2,3-dimethyl pentene-Z; 3-methyl-2-ethyl butene-l and 2,3-dimethyl heptene-2, thereby producing a predominance of 2,3- dimethyl butadiene-1,3.

7. A process according to claim 1 in which the olefin is at least one selected from the group of 3,4-dimethyl hexene-2 and S-methyl heptene-3, thereby producing a predominance of 2-methyl pentadiene-1,3.

8. A process according to claim 1 in which the olefin is at least one selected from the group of 2,4-dimethyl pentene-Z; Z-methyl heptene-3 and 2-propyl pentene-2, thereby producing a predominance of 2-methyl pentadicue-1,3 and 4-methyl pentadiene-1,3.

9. A process according to claim 1 in which the olefin is at least one selected from the group of Z-methyl pentene-2; B-methyl pentene-2; 2-ethy1 butene-l; 2,3-dimethyl butene-l; 2-methyl heXene-Z and 3-methyl heXene-Z, thereby producing a predominance of isoprene.

10. A process according to claim 9 in which the bromine'containing compound is hydrogen bromide.

References Cited FOREIGN PATENTS 156,122 3/1922 Great Britain. 807,149 1/1959 Great Britain. 868,566 5/1961 Great Britain.

PAUL M. COUGHLAN, JR., Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No 3,388 ,183 June 11, 1968 Kenneth J. Frech It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 6, line 43, "Z-methyl pentadiene lfi" should read 3*methy1 pentadiene1,3

Signed and sealed this 25th day of November 1969.

(SEAL) Attest:

Edward M. Fletcher, Jr. WILLIAM Attesting Officer Commissioner of Patents 

